1. Field of the Invention
The present invention relates to a vibration type driving apparatus comprising a vibration body which generates vibration by supplying a driving signal to an electro-mechanical energy converting element such as a piezoelectric element and a contact body which contacts the vibration body.
2. Description of the Related Art
Many proposals concerning a vibration type driving apparatus including an oscillatory wave motor, etc., have so far been presented.
For example, Japanese Patent Laid-Open No. S60(1985)-174078 discloses a vibration type driving apparatus provided with a disk type vibrator with a piezoelectric element, which is an electro-mechanical energy converting element, bonded to its bottom surface, wherein ring-shaped protrusions are formed on the surface of the vibrator, these ring-shaped protrusions are placed at locations of the vibrator where displacement of an oscillatory wave produced on the vibrator reaches a maximum and a rotor contacts these protrusions.
Furthermore, Japanese Patent Laid-open No. 2002-142472 discloses a vibration type driving apparatus provided with a circular ring vibrator with a piezoelectric element, which is an electromechanical energy converting element, bonded to its bottom surface, wherein when a driving signal is supplied to the piezoelectric element, standing waves with phase A and phase B of the same degree with a phase shift of 90 degrees are generated, combining these standing waves produces a traveling wave on the surface of the vibrator, the vibrator is provided with a protrusion for enlarging vibration displacement of the traveling wave and a rotor contacts these protrusions.
Furthermore, U.S. Pat. No. 6,559,574 discloses a vibration type driving apparatus provided with a vibrator with a laminated piezoelectric element fixed between two elastic bodies made of metal, etc., wherein when a driving signal is supplied to the piezoelectric element, standing waves with phase A and phase B of the same degree with a phase shift of 90 degrees are generated, combining these standing waves causes the vibrator to start oscillation, generates a primary traveling wave on the surface of the vibrator and a rotor contacts the end surface of this vibrator.
In the vibration type driving apparatus described in Japanese Patent Laid-Open No. S60(1985)-174078, a protrusion contacting the rotor is formed at a position substantially a midpoint between the center and outer edge of the vibrator where vibration displacement reaches a maximum. In this configuration, the diameter of a circle formed by contact points between the vibrator (protrusion) and the rotor becomes substantially half the diameter of the vibrator.
In this vibration type driving apparatus, the diameter of the circle formed by contact points between the vibrator and the rotor constitutes one of factors which determine the output and trying to increase the output results in an increase in the diameter of the vibrator (increase in size of the apparatus).
In contrast, in the vibration type driving apparatus described in Japanese Patent Laid-Open No. 2002-142472, the piezoelectric element and protrusion are arranged on the same circular ring, and therefore the diameter of a circle formed by contact points between the vibrator (protrusion) and rotor can be substantially equal to the diameter of the vibrator. However, compared to the size of the entire vibrator, the area occupied by the piezoelectric element is small.
On the other hand, the vibration type driving apparatus described in U.S. Pat. No. 6,559,574 has a laminated piezoelectric element fixed between two elastic bodies, and therefore the area of the laminated piezoelectric element can be relatively large compared to the size of the vibrator. Furthermore, the driving surface on which the vibrator contacts the rotor can have substantially the same outer diameter as the circumference of the vibrator. However, suppressing the natural frequency of vibration to a practical value requires the dynamic rigidity of the vibrator to be reduced and requires the length of the vibrator in the axial direction to be large to a certain extent (increase in size of the apparatus).
As shown above, the conventional vibration type driving apparatuses have difficulty in further reducing the size of the apparatus while maintaining output at a practical level.